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CSharp · Console

/Program.cs

using System;
using System.Text.RegularExpressions;
					
public class Program
{
	public static void Main()
	{
		string Case1 = "123E";
		Regex rgx = new Regex(@"^\d{3}[a-zA-Z]$", RegexOptions.ECMAScript);
		Console.Write(rgx.IsMatch(Case1));
	}
}